An ink-jet printer includes one or more ink cartridges that contain ink. In some designs, the cartridge has discrete reservoirs of more than one color of ink. Each reservoir is connected via a conduit to a print head that is mounted to the body of the cartridge.
The print head is controlled for ejecting minute droplets of ink from the print head to a printing medium, such as paper, that is advanced through the printer. The ejection of the droplets is controlled so that the droplets form recognizable images on the paper.
The ink droplets are expelled through orifices that are formed in an orifice plate that covers most of the print head. The orifice plate is typically bonded atop an ink barrier layer of the print head. That layer is shaped to define ink chambers. Each chamber is aligned with, and continuous with, an orifice from which the ink droplets are expelled.
The ink droplets are expelled from an ink chamber by a heat transducer, such as a thin-film resistor. The resistor is carried on an insulated substrate, which is preferably a conventional silicon wafer upon which has been grown an insulation layer, such as silicon dioxide. The resistor is covered with suitable passivation and other layers, as is known in the art and described, for example, in U.S. Pat. No. 4,719,477, hereby incorporated by reference.
The resistor is selectively driven (heated) with a pulse of electrical current. The heat from the resistor is sufficient to form a vapor bubble in an ink chamber, thereby forcing a droplet through the associated orifice. The chamber is refilled after each droplet ejection with ink that flows into the chamber through a channel that connects with the conduit of reservoir ink.
Color printing on white media is accomplished by using at least three different colors of ink: cyan, yellow, and magenta. These three colors can be combined to form the color black. For efficiency reasons, however, a separate supply of black ink is normally provided.
Print quality is generally improved when, among other things, one can precisely control the volume of the individual ink droplets that are expelled from the print head. More specifically, print quality is enhanced in instances where the volume of one color of ink droplet can be controlled relative to the volume of another color of ink droplet. For example, to produce a blue dot, a droplet of cyan ink and a droplet of magenta ink are expelled to the same location of the print media. A black dot is made with a single droplet of black ink. In order to ensure that the blue dot (or any other two-component color) is not unacceptably large, the ink chambers and/or orifices of the print head can be designed so that the black ink droplet is about twice as large as the droplets produced for the cyan, yellow and magenta inks.
Other important design considerations for ink-jet printers concern what is known as turn-on energy or TOE. This refers to the amount of energy required by a resistor for heating the ink in a chamber by an amount sufficient to create a vapor bubble for expelling a droplet of ink. It is desirable to minimize the TOE, primarily to minimize the operating temperature of the print head and avoid the problems associated with a high operating temperature, such as the creation of air bubbles in the ink.
Chamber refill times can be limiting factors as respects the overall throughput of the printer because the frequency with which the ink chamber can be refilled limits the frequency with which droplets can be expelled. It is also important that the ink chamber and connected channel are configured in a way such that flow of ink to refill the chamber settles as quickly as possible so that the ejected droplet will not be affected by any wave action of the ink in the chamber.
One way to meet the above-noted design considerations is to modify the shape of the orifices, ink chambers, and ink channels. In the past, the barrier layer in which the chambers were formed was applied as a single layer, having a uniform depth across the area of the print head. A uniform-depth orifice plate was attached to the barrier layer. As a result, one interested in modifying the shape of one chamber relative to another chamber was limited to changing the length or width of the chamber. Likewise, one orifice size could be changed relative to another by changing its diameter, but not its depth.
The present invention expands the options for ink-jet print head designers. The invention is directed to a method for making the orifice plate of an ink-jet printer that defines both the orifices and the ink chambers. The orifice plate is constructed to permit, in the same print head, one chamber to be deeper (as well as, if desired, wider and longer) than another chamber that may be next to the first chamber. Similarly, the channel delivering ink to the first chamber may be configured to be deeper or shallower, as needed, relative to another channel on the print head.
The advantages of the present invention are best considered in connection with a preferred embodiment of an ink-jet cartridge that carries reservoirs of four color sets of ink: cyan, yellow, magenta, and black. The chamber-, orifice-, and channel-shape variations provided by the present invention can be made to one color set of chambers, channels, and/or orifices relative to another color set. For example, the ink chambers associated with the black ink can be made deeper than the chambers associated with the cyan ink.
A preferred method for carrying out the present invention uses a layer of photoresist material as both the orifice plate and barrier. That material is exposed with electromagnetic radiation (such as UV light) in a way that varies, across the area of the orifice plate, the intensity of the radiation to thus vary the depth of polymeric cross-linking that occurs in the layer. This allows one to select, via arrangement of exposure-controlling mask(s), different sizes of the ink chambers, etc. in the same orifice plate.
Other advantages and features of the present invention will become clear upon study of the following portion of this specification and the drawings.